Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.57   10.186%   $64.5359   $64.54   $64.55   $64.50  
  Purchase #2 $160.94   10.231%   $177.4058   $177.41   $177.40   $177.40  
  Purchase #3 $216.92   4.241%   $226.1196   $226.12   $226.10   $226.10  
  Purchase #4 $68.94   6.579%   $73.4756   $73.48   $73.50   $73.50  
  Purchase #5 $193.32   10.833%   $214.2624   $214.26   $214.25   $214.30  
  Purchase #6 $176.43   12.823%   $199.0536   $199.05   $199.05   $199.10  
  Purchase #7 $92.77   4.760%   $97.1859   $97.19   $97.20   $97.20  
  7 purchase totals = $967.89       $1,052.0388   $1,052.05   $1,052.05   $1,052.10